Computer simulation of the thermal mechanics of steel quenching

Thermal stresses and associated component distortion remains one of the major problems that perplex heat treaters. It may become more significant when dealing with quenching processes, a dominant method of hardening materials in heat treatment. Excessive distortion or even fracture is one of the biggest problems associated with quenching processes, which not only increases the cost of the production but may also directly impair the quality of the heat treated components. Past work focusing on steel quenching has been experimental in nature with emphasis on experimental tests, material selection, cycle design, quenchant selection and quenching equipment design. This traditional methodology has some limitations including significant expense and difficulty of extending accumulated experience to applications other than those from which the data was derived. Mathematical modeling and computer simulation has developed rapidly in recent history, especially with the evolution of high-speed digital computers. Thanks to the rapid development of various numerical analysis software and the speed of computer hardware, large scale and sophisticated models can now be analyzed routinely. Nevertheless, difficulties still exist which stem from uncertainties in the theories and processes, limited availability of representative physical and mechanical property data, complexities of boundary conditions and excessive cost and time required for modeling procedures.; Mathematical modeling and computer simulation forms a virtual laboratory platform for quenching analysis. Important issues on process modeling in quenching practice, including the quenching model and its implementation will be discussed and presented. Work in this study focused on liquid quenching involving oil, polymer and water quenching. The challenges and limitations of process modeling of steel quenching will be discussed from both theoretical and practical perspectives. Standardized methodology of studying heat transfer behavior between the quenchant and quenched component, specifically, the quenching probe, were studied, especially the method involving lumped capacitance analysis for deriving heat transfer coefficients. A numerical validation procedure was proposed and implemented. Limitations of the standard lumped capacitance model were analyzed quantitatively. A modified lumped capacitance method was developed and implemented in a numerical analysis procedure and validated against experimentally derived results. Significant improvement was achieved especially for low-to-moderate sensitivity quenching probes.; A weakly coupled numerical modeling procedure was proposed to predict the effectiveness of a new quenching cycle for a practical application. Temperature fields of the quenching process were simulated and results were in good agreement with those derived experimentally. Phase transformation products and residual stresses were predicted and their implications discussed with respect to the quenching conditions. The validity of the quenching cycle was examined critically and deemed acceptable with the aid of computer simulations and predictions. The role of the computer in process modeling was examined and discussed. Two application tools for facilitating heat treatment process modeling practice were developed and tested against well-established experimental standards. Development and use of relational database and object-oriented database procedures in process modeling practice was explored. The objective of incorporating database applications in this study was to initiate an efficient and systematic method for modeling practice so that process related data and results could be stored and/or retrieved efficiently.